The invention pertains to geometrical instruments, more particularly those that locate the vertical center line of three dimensional objects having circular horizontal cross section, and most particularly those that locate the focal axis of parabolic antennas.
A general problem with widespread applicability to surveying instruments is the location of the normal axis of circular symmetry of an object having a horizontally disposed circular cross section. As with any geometrical instrument, precision on the one hand, and ruggedness for field use on the other, are critical determinants of the usefulness or uselessness of such instruments. This is especially true for the installation of parabolic antennas, which are objects of circular revolution about a central focal axis. The antenna's focus, located on the focal axis, is the point at which the antenna's feed or pickup must be disposed. As such an antenna is used with increasingly higher frequencies, smaller errors in placement of the feed or pickup can result in significant degradation of the antenna's performance. Moreover, small deformations in such an antenna's surface can have a significant effect on antenna performance especially at high frequencies, but the process of locating the antenna's focus and installation of the feed or pickup often requires the antenna's surface to support the significant weight of a centering instrument, a technician, or both, weight which can easily damage the antenna's surface.